An OTN (Optical Transport Network) is standardized as a framework in an optical network field adopting a WDM (Wavelength Division Multiplexing) technology. The OTN is capable of accommodating a plurality of client signal types and is capable of transmitting a large amount of client signals. Japanese Patent Application Publication No. 2008-113395 discloses an optical transmission system accommodating and multiplexing client signal in an OTU (Optical Transfer Unit) frame of an OTN and transmitting the accommodated and multiplexed client signal.
Recently, standardization of Ethernet having a bit rate of approximately 100 Gbps is being reviewed as a next generation Ethernet with respect to the Ethernet that is one of main client signals. An OTN requires a frame accommodating and transmitting 100 Gbps bit rate Ethernet signal. The OTN requires a frame multiplexing, accommodating and transmitting a plurality of signal types having a bit rate lower than 100 Gbps.